PROJECT ABSTRACT Microtubules (MT) are the target of paclitaxel, the most widely prescribed drug for the breast and ovarian cancers. Paclitaxel acts by stabilizing microtubules which results with cell death. The inability to predict and influence how cancer patients will respond to paclitaxel represents a major clinical problem. UNC-45A is a member of the UCS protein family of myosin II co-chaperones. Recent evidences including our recently published data show that, in addition to regulating actomyosin contractility, UNC-45A is also a MT destabilizing protein. In human cancers UNC-45A overexpression correlates with poor outcome. A significant contributor to poor patient outcomes is chemoresistance to paclitaxel. Here we want to investigate whether and how UNC-45A confers cancer cells? a cellular survival advantage upon paclitaxel treatment. Aim 1. Determine the contribution of UNC-45A in paclitaxel resistant human cancers. We will (a) Determine whether UNC-45A overexpression is a predictor of paclitaxel resistance in ovarian and breast cancer clinical specimens, and (b) Determine whether in cancer cells derived from ovarian and breast cancer patients, UNC-45A regulates cells? sensitivity to paclitaxel. Aim 2. Determine the biophysical and cell biological parameters of MT regulation by UNC-45A. We will (a) Determine the binding, localization properties and MT destabilizing effects of UNC-45A on MTs in the presence and absence of paclitaxel, (b) Perform computational modeling to evaluate a mechanistic connection between UNC-45A localization and MT stability and, (c) Determine the effects of UNC-45A on MT dynamics in living cells. Aim 3. Determine the biochemical basis of UNC-45A?s effect on MTs. We will (a) Determine whether UNC- 45A oligomerizes in vitro and binds to MTs as an oligomer (b), and (c) Determine the domain(s) of UNC-45A that are involved in MT-binding, MT-destabilization and oligomerization. RELEVANCE: Our studies will provide us with a new biomarker and molecular target for paclitaxel-resistant human cancers, a deep understanding of the mechanistic interaction between this novel ATP-independent protein and MTs, and a platform for development of novel therapeutic targets including small molecule inhibitors of protein-protein (oligomer) interactions.